Laser projectors without a projection optical system having a micromirror unit which scans a projection surface (scanning mirror laser projectors) are known. In the near future, the mentioned micromirror units will play an important role in projection devices, in particular miniaturized projectors. Of the various technologies used for providing a pico projector, laser scanning devices offer several advantages, such as a small design and an increased efficiency due to the fact that the laser light is emitted only when it is actually needed. The generated images are advantageously very bright due to the bright colors that come from laser sources. A known disadvantage of the mentioned laser light sources is the so-called “speckle effect,” which is caused by interferences between the laser beam and a projection surface and which results in a plurality of light spots having different brightness levels.
An improvement in the form of reducing the mentioned speckle effect lies in using laser diodes instead of solid-state lasers.
To even further reduce the speckle effect, a high modulation rate of the laser light of the laser diode in the range of several 100 MHz may be used to keep a speckle contrast ratio for an observer within an acceptable level. However, as the result of using this type of modulation, the base spectral line width is too narrow to achieve an acceptably low contrast ratio for the speckle effect. Higher modulation rates in the range of 1 GHz are not easily integratable into a consumer article having a device, for example projectors, or a mobile telephone, a camera, or a laptop.
Therefore, there is a need for efficient reduction of the speckle effect.